1. Field of the Invention
This invention relates to fibers having improved liquid absorption capacity combined with the ability to provide a dry feeling even when nearly saturated.
2. Description of the Related Art
Articles having liquid absorption capabilities have found diverse applications in areas such as diapers, incontinent briefs, feminine hygiene napkins, tampons, surgical sponges, wound dressings, towels, separation of oil from the surface of water, and the containment or collection of oil in industrial installations. Generally, the utility of such articles is based on fibers having suitable absorbent structures.
Absorbent fibers have been described for example in U.S. Pat. Nos. 4,707,409; 5,057,368; 5,124,205; 5,200,248; 5,268,229; 5,496,627; 5,972,505; 5,977,429; 6,093,491; 6,296,821B1 and in WO 98/07909. U.S. Pat. No. 4,707,409 describes a filament with a four-winged cross-section. U.S. Pat. No. 5,057,368 describes multilobal fibers wherein each lobe has a leg and a cap. U.S. Pat. No. 5,124,205 describes a grooved filament wherein the surface roughness at the bottom of a groove is greater than outside of the groove. The surface roughness is produced by a chemical etching technique. U.S. Pat. No. 5,200,248 describes capillary channel structures having a xe2x80x9cSpecific Capillary Volumexe2x80x9d of at least about 2.0 cc/g and a xe2x80x9cSpecific Capillary Surface Areasxe2x80x9d of at least about 2000 cm2/g. U.S. Pat. No. 5,268,229 describes filaments having xe2x80x9cUxe2x80x9d and xe2x80x9cExe2x80x9d shaped cross-sections with stabilizing legs. U.S. Pat. No. 5,496,627 describes filaments having a xe2x80x9ccross-sectional shape factorxe2x80x9d greater than 1.5 and a specific volume of about 1.5-5 cc/g. U.S. Pat. No. 5,972,505 describes fibers having arms extending from both sides of a central spine. U.S.P. describes fibers 2 to 37 mm in length and having varying cross-sectional shapes along their length. U.S. Pat. No. 6,093,491 describes grooved filaments where the cross-sectional area of the groove is greater than or equal to xcfx80/8 times the square of the width of the groove mouth. WO 98/07909 describes a bundle of synthetic fibers wherein the filaments comprising the bundle have a xe2x80x9cSingle Fiber Bulk Factorxe2x80x9d greater than 4.0, the bundle has a xe2x80x9cSpecific Volumexe2x80x9d greater than 4.0 cc/g and certain xe2x80x9cMaximum Potential Fluxxe2x80x9d values.
Each of the fibers cited above represented progress toward the goals to which they were directed. However, none described the specific constructions of the present invention and none satisfied the needs met by this invention. A need exists for fibers that have high liquid absorption capacity combined with the ability to provide a dry feeling even when nearly saturated.
The invention provides novel fibers for use in applications such as diapers, incontinent briefs, feminine hygiene napkins, tampons, surgical sponges, wound dressings and towels and in applications such as flotation booms suitable for the containment and collection of oil from the surface of water, and filters for the collection of oil from aqueous liquids.
The fibers of the invention having improved liquid absorption capability are comprised of a plurality of filaments having one or more capillary channels. Each such capillary channel is formed by capillary channel walls, and has a channel-opening dimension. The filaments comprising the fibers of the invention satisfy the following equations:
0.1xe2x89xa6Af/AfPxe2x89xa60.8xe2x80x83xe2x80x83Eq. 1
0.1xe2x89xa6xcexa8xe2x89xa61xe2x80x83xe2x80x83Eq. 2
1xe2x89xa6dxe2x89xa680xe2x80x83xe2x80x83Eq. 3
1.75xcexa8xe2x88x920.83 Af/AfPxe2x88x920.017 d+1.48xe2x89xa70xe2x80x83xe2x80x83Eq. 4
wherein
Af is the cross-sectional area occupied by the material comprising the filament;
AfP is the footprint area of the filament cross-section;
d is the denier of the filament;
xcexa8 is the ratio of the square root of the sum of the cross-sectional areas of the channels in a filament to the sum of the channel opening dimensions as expressed by following equation;                     Ψ        =                                                            ∑                                  i                  =                  1                                N                            ⁢                              xe2x80x83                            ⁢                              Ac                ⁢                                  xe2x80x83                                ⁢                                  (                  i                  )                                                                                        ∑                              i                =                1                            N                        ⁢                          xe2x80x83                        ⁢                          L              ⁢                              xe2x80x83                            ⁢                              (                i                )                                                                        Eq        .                  xe2x80x83                ⁢        5            
xe2x80x83wherein
Ac(i) is the cross-sectional area of the ith channel;
L(i) is the dimension of the opening of the ith channel;
N is the number of channels; and
wherein the fiber has a liquid absorption capacity of at least about two volumes of liquid per volume of fiber.